To improve communication reliability, it is necessary for improving quality of service of communication system and establishing standbys for communication system or backup for communication data.
The networking structure of an existing communication access network is shown in FIG. 1. The communication access network includes: a user terminal, an access layer device, a transfer device and a convergence layer device.
The access layer device connects with the convergence layer device via the transfer device. The connection of the access layer device and the user terminal is generally shown in FIG. 2 including setting a Main Distribution Frame (MDF) between the access layer device and the user terminal, and the MDF is responsible for the jumper connection between the access device and a subscriber line.
The user terminal such as telephone terminal, dialing Modem and Asymmetrical Digital Subscriber Loop (ADSL) Modem, is located nearby the subscriber side. The user terminal is responsible for transferring various signals of a subscriber to the access layer device.
The access layer device is responsible for receiving various signals transferred by the user terminal, converting the various signals into signals that can be handled by the system, and transmitting the signals to the convergence layer device at the network side via the transfer device.
The access layer device may include a narrowband access device, a broadband access device and an integrated access device which are different in functions. The narrowband access device is developed earliest. The narrowband access device provides access functions of such services as Plain Old Telephone Service (POTS), Integrated Services Digital Network (ISDN) and sub-rate link. The broadband access device is developed lately. The broadband access device may be a Digital Subscriber Line Access Multiplexer (DSLAM). And the DSLAM includes an Asynchronous Transfer Mode (ATM) DSLAM and an Internet Protocol (IP) DSLAM. The DSLAM connects a subscriber and a network through xDSL access technique, and the uplink interface thereof is respectively an ATM interface and an IP interface. The integrated access device is an inter-grade device form between the narrowband access device and the broadband access device. The integrated access device each provides access functions for narrowband services and broadband services simultaneously.
The convergence layer device is responsible for converging various data of the subscriber and transferring the data to a core network.
A failure may occur in a line card of the access layer device, for example a port of the line card is in failure or the whole line card is in failure. When one port of the line card is in failure, other ports may still function. For the failure mode, manufacturers set forth the concepts of ‘N+1’ port standby and ‘N+1’ card standby.
For the ‘N+1’ port standby, if a port of the line card is in failure, switch the subscriber service of the port to a standby port of the line card which replaces the port to continue the work, so the continuity of service is guaranteed.
For the ‘N+1’ card standby, if a card of the access layer device is in failure and is unable to serve, an Element Management System (EMS) switches all the subscribers of the card including subscriber lines and subscriber data to a standby line card of the EMS to enable the subscribers to continue enjoying services.
In an existing solution, the ‘N+1’ card standby is implemented by integrating a relay matrix on a card of the splitting box (SPL box) which is equipped externally, and the implementation scheme includes:
defining a set of standby buses on a backplane, connecting all subscriber line interfaces of the card to the standby buses via the relay matrix, outputting the standby buses via a specific standby line card to implement the standby function.
As can be seen from the above technical scheme, the ‘N+1’ card standby needs the SPL box, which limits the application.
In another existing solution, the ‘N+1’ port standby is implemented through the relay matrix integrated on the line card, and the implementation scheme includes: forming a standby channel by internally or externally testing the relay matrix on the line card, and implementing the ‘N+1’ port standby function.
As can be seen from the above technical scheme of the existing art, only the ‘N+1’ port standby is implemented; the implementation of the ‘N+1’ card standby requires that signals of all ports of a line card should be connect to a standby line card from the backplane via connectors, the amount of connectors and the layer of the backplane is great, which makes the ‘N+1’ card standby difficult to be implemented.